1. Field of the Invention
The present invention relates to processing of high temperature superconductor ceramic materials and processing of semiconductor integrated circuits.
2. Background of the Related Art
Achievement of superconductivity at high temperature, i.e. temperatures greater than that of liquid nitrogen, is of tremendous technological importance. The number of potential applications for such high temperature superconductors are clearly enormous. Therefore, the announcement of superconductivity at approximately 30 K by Bednorz and Muller, Z. Phys. B. 64, 189 (1986) in certain lanthanum barium cupric oxide ceramic materials has generated unprecedented excitement and efforts in the scientific, technological and business communities. Following the announcement of the work of Bednorz and Muller, these efforts have generated several significant and rapid increases in the superconductivity onset temperatures. Chu and others have reported superconductivity over 90.degree. K. in yttrium barium cupric oxide ceramic compounds. M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, C.J. Huang, Y.Q. Wang, and C.W. Chu, Phys. Rev. Lett. 58, 908 (1987), C.W. Chu, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang and Y.Q. Wang, Phys. Rev. Lett. 58, 408 (1987). More recently, superconductivity at 155 K with evidence of superconductivity onset above room temperature has been reported S.R. Ovshinsky, R.T. Young, D.D. Allred, G. DeMaggio, G.A. Van der Leeden, Phys. Rev. Lett. 58, 2579 (1987). The latter result involved a multiphase ceramic material of yttrium, barium, copper, fluorine and oxygen.
A significant problem associated with forming circuits from the new high temperature superconductors, however, is the high processing temperature required for forming the superconducting ceramic materials, typically in the range of 700.degree. to 1000.degree. C. These temperatures are higher than can be withstood by silicon or gallium arsenide materials used as part of hybrid semiconductor/superconductor circuits. Therefore, to form a hybrid semiconductor/superconductor circuit, temperatures should be maintained below 450.degree. C. to avoid breakdown of the silicon employed in such a silicon/superconductor hybrid circuit. However, this temperature is too low for formation of superconductor layers on the silicon since these would require temperatures in the 900.degree. to 1000.degree. C. range.
Another problem related to the processing of hybrid semiconductor/superconductor circuits, using conventional semiconductor processing techniques, is the tendency of the high temperature ceramic superconductors to lose oxygen in a vacuum environment and thereby lose superconducting properties. For this reason, conventional vacuum deposition techniques cannot be employed for depositing the ceramic superconductor materials onto a semiconductor substrate in a conventional manner.
For the foregoing reasons, a strong need presently exists for a method for forming hybrid semiconductor/superconductor circuits using some or all of the already highly developed semiconductor processing technology.